msgget - get message queue
int msgget(key_t key, int msgflg);
msgget returns the message queue identifier associated with key.
A message queue identifier and associated message queue and data
structure [see intro(2)] are created for key if one of the following are
key is IPC_PRIVATE.
key does not already have a message queue identifier associated with
it, and (msgflg<b>&IPC_CREAT) is true.
On creation, the data structure associated with the new message queue
identifier is initialized as follows:
msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_perm.gid are set
to the effective user ID and effective group ID, respectively, of
the calling process.
The low-order 9 bits of msg_perm.mode are set to the low-order 9
bits of msgflg.
msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime are set to
msg_ctime is set to the current time.
msg_qbytes is set to the system limit.
msgget fails if one or more of the following are true:
EACCES A message queue identifier exists for key, but operation
permission [see intro(2)] as specified by the low-order 9
bits of msgflg would not be granted.
ENOENT A message queue identifier does not exist for key and
(msgflg<b>&IPC_CREAT) is false.
ENOSPC A message queue identifier is to be created but the
system-imposed limit on the maximum number of allowed
message queue identifiers system wide would be exceeded.
EEXIST A message queue identifier exists for key but
(msgflg<b>&IPC_CREAT) and (msgflg<b>&IPC_EXCL) are both true.
intro(2), msgctl(2), msgop(2), stdipc(3C).
Upon successful completion, a non-negative integer, namely a message
queue identifier, is returned. Otherwise, a value of -1 is returned and
errno is set to indicate the error.
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